As industry has continued to refine and improve production techniques and procedures, corresponding requirements have been levied for placing identifying, data related markings upon components of manufactured assemblies. With such marking, the history of a product may be traced throughout the stages of its manufacture and components of complex machinery such as automobiles and the like may be identified, for example, in the course of investigations by governmental authorities.
A variety of product marking approaches have been employed by industry. For example, paper tags or labels carrying bar codes may be applied to components in the course of their assembly. For many applications, such tags or labels will be lost or destroyed. Ink or paint spraying of codes such as dot matrix codes have been employed for many manufacturing processes. Where the production environment is too rigorous, however, or subsequent painting steps are involved, such an approach has been found to be unacceptable.
The provision of a permanent or traceable marking upon hard surfaces such as metal traditionally has been achieved with marking punches utilizing dies which carry a collection of fully formed characters. These "full face dies" may be positioned in a wheel or ball form of die carrier which is manipulated to define a necessarily short message as it is dynamically struck into the material to be marked. As is apparent, the necessarily complex mechanisms involved are prone to failure and full face dies exhibit rapid wear. Generally, the legibility and abrasion resistance of the resultant marks can be considered to be only fair in quality. Additionally, the marking punch approach is considered a poor performer in marking such surfaces as epoxy coatings and the like.
Laser activated marking systems have been employed. However, such systems are of relatively higher cost and the abrasion resistance and "readability after painting" characteristics of laser formed characters are considered somewhat poor.
U.S. Pat. No. 4,506,999 by Robertson, issued in 1985, entitled "Program Controlled Pin Matrix Embossing Apparatus" describes and claims a computer driven dot matrix marking technique which has been successful in the marketplace. This marking approach employs an array of tool steel punches which are uniquely driven using a pneumatic floating pin impact concept to generate man readable and/or machine readable dot characters or codes. Marketed under the trade designation "PINSTAMP", these devices carry the noted steel punches or "pins" in a head assembly which is moved relative to the workpiece being marked at selected skew angles to indent a dot or pixel defining permanent message or code into a surface. The system enjoys the advantage of providing characters of good legibility as well as permanence. Additionally, a capability for forming the messages or codes during forward or reverse head movements is realized. Use of the basic dot matrix character stamping device is limited, however, to piece parts which are both accessible and of adequate size.
Robertson, et al., in U.S. Pat. No. 4,808,018, entitled "Marking Apparatus with Matrix Defining Locus of Movement", issued Feb. 28, 1989, describes a dot matrix character impact marking apparatus which is capable of forming messages or arrays characters within a very confined region. With this device, a linear array of marker pins is moved by a carriage in a manner defining an undulating locus of movement. This locus traces the matrix within which character fonts are formed by the marker pins. The carriage and head containing the marker pins are pivotally driven by a cam to provide vertical movement and by a Geneva mechanism to provide horizontal movement. Pixel positions for the matrices are physically established in concert with pin or carriage locations by a timing disk and control over the pins is generated in conjunction with an interrupt/processor approach. Each marking pin of the pin array within the head assembly of this portable device is capable of marking more than one complete character for a given traverse of the head between its limits of moment.
Robertson, et al., in U.S. Pat. No. 5,015,106, issued May 14, 1991, and entitled "Marking Apparatus with Multiple Line Capability" describes a dot matrix character impact marking apparatus which achieves a multiple line capability wherein a carriage component carrying one or more marker pin cartridges moves within a singular plane locus of movement. This multiple line capability advantageously has permitted a broad variety of line configurations, for example in widely spaced positions at a workpiece. The device further employed a retrace method in generating a locus of marking movement somewhat similar to the formation of a raster in conjunction with television systems. A modular approach for the device was provided utilizing a forward housing carrying the locus defining component of the device which was then actuated from a rearwardly disposed motor containing housing component which served to drive cam assemblies at the forward portion. The carriage component of the device carried a manifold which, in turn, carried one or more marker pin cartridges, the pins of which were driven from an externally disposed valved and pressurized air supply. As before, the device performed in conjunction with a predetermined character defining matrix of pixel positions, each position of the matrix being identified to the system by a timing disk physically maneuvered with the drive components.
The success of the above products has led to further calls on the part of industry for even more compact marking systems of lower weight and higher rates of marking speed. Further, interest has developed in providing a broad range of marking capabilities for the type devices at hand. Robertson, et al., in U.S. Pat. No. 5,316,397, entitled "Marking Apparatus With Multiple Marking Modes", issued May 31, 1994, describes a matrix form of character marking utilizing a single plane undulatory motion of the pin cartridge carrying carriage, as well as a capability for the above-described raster form of locus of movement. This flexibility is achieved through the utilization of software changes as opposed to the insertion of hardware-based timing components and the like. The system disclosed exhibits a capability for full form character formation. This requires the actuation of the marker pins in a manner wherein discrete dots or pixels are not observable, the indentations formed by these pins being so closely nested as to evoke the image of a continuous line forming each character.
The floating pin impact concept initially introduced by Robertson has led to a variety of applications on the part of investigators. For example, in Cyphert, et al., U.S. Pat. No. 5,167,457, entitled "Apparatus and Method for Marking Arcuately Configured Character Strings", issued Dec. 1, 1992, and assigned in common herewith, the marking approach is adapted to the formation of character strings in arcuate fashion. Similarly, the approach was adapted to systems for marking the curved inner surface of pipes as described in U.S. Pat. No. 5,119,109, by Robertson, entitled "Method and Apparatus for Marking the Inside Surface of Pipes", issued Jun. 2, 1992, and assigned in common herewith.
The reading of dot matrix characters and codes following their formation may be carried out by a video based system described in U.S. Pat. No. 4,806,741, by Robertson, entitled "Electronic Code Enhancement for Code Readers", issued Feb. 21, 1989, and assigned in common herewith.
Certain marking applications of the floating pin impact concept call for the use of a single marking pin as opposed to an array of pins. Guidance of this form of single pin typically has been carried out utilizing robotic systems. One such system currently is marketed under the trade designation "TMP 6000" by Telesis Marking Systems, Inc., of Circleville, Ohio.
Investigators now are seeking to improve the performance of these marking systems in terms both of speed and dot or indentation quality. Speed of marking generally is constrained by the air pressure limits of solenoid actuated valves and delivery systems. Thus, enhancements of this operational parameter have been sought to be achieved with efficient valve actuation and improved pin-cartridge design. Dot quality aspects involve both the controlled depth of the dot formation, as well as proper positioning of the dot in the construction of character symbols and codes. Heretofore, the hardened steel pins employed with the arrays have been slidably mounted within chambers formed in steel or surface hardened aluminum cartridges. These cartridge chambers have been observed to wear, a condition leading to degrading pin marking performance. Lubrication for the rigorous pin dynamics involved has been through the introduction of lubricant into driving and return air functions of the system. Poor control over the amounts of such lubricant employed leads to undesirable variations in the quality of dot formation. In general, the structures which have been heretofore developed have been of a somewhat robust nature in view of the forces involved in driving the pins into impact with a metal surface and the return of the pins. Where a pin "misses" or fails to strike a surface to be marked, then impact dynamics are visited upon the marking system. Such dynamics must be accommodated in any design. Of current interest, it has been apparent that it is desirable to expand the utilization of this form of marking to the identification of components of a broader variety of products. This calls for the development of marking systems which retain the quality of marking heretofore achieved, but which are of lesser cost and, preferably, which are much lighter, notwithstanding the dynamics of character formation involved.